Using Doppler velocity spectra to study the formation and evolution of ice in a multilayer mixed-phase cloud system

Mixed-phase clouds are prevalent in the Arctic. Although these clouds are observed during all the seasons of the year, they are most frequent in the spring and the fall seasons, when they can occur for long periods. The correct partition of the two phases of water in these clouds is necessary for accurate determination of the energy balance at the surface. However, factors that govern the formation and the evolution of the two phases in these clouds are poorly understood. Even less understood are the complicated, but common, multi-layer mixed-phase clouds.

The Mixed-Phase Cloud Experiment (M-PACE), which was funded by the Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) program, was conducted from 27 September to 22 October 2004. An objective of M-PACE was to acquire a data set that would improve the understanding of all the stages of the mixed-phase cloud life cycle.

We analyze the microphysical and macrophysical characteristics of a multilayer mixed-phase cloud system, observed on the 6th of October 2004. Doppler spectra obtained from the ARM millimeter wavelength radar (35 GHz) located at Barrow are used to separate the contributions of different hydrometeor populations to the total reflectivity: i.e., contributions from liquid droplets and a few ice populations. During the period of our analysis, we observe ice precipitation that originates in the higher-level cloud decks; somewhat surprising is the identification of a few low-level liquid cloud layers that are embedded in the ice precipitation yet remain not glaciated. In the same period, we detect ice that forms and falls out of these embedded low-level liquid layers. We determine how the ice precipitation that falls into these low-level liquid layers affects them and their ice production.